"tunic" wrote in message
lkaboutpets.com...
hello,

my cat (male, 3.5 years old) had urethra blockage twice before (in a 1.5
year period) due to struvite crystal formation in his bladder
he has been on a specific diet (hills c/d) which is a low-magnesium
acidifying food in order for the crystals to be dissolved. he was also fed
another acidifying medicine (named methygel)

yesterday he had another blockage, i took him to the vet and he has been
catheterized. the vet took urine samples and measured the pH which was
very acidic (6) and checked them at the microscope but couldnt definitely
determine if the crystals were sturvite or calcium ocalate. one logical
explanation is that the acidifying diet aimed at struvite crystals made
way for the formation calcium oxalate ones. but the clues tend to
sturvite..

my questions a
1. is it possible for sturvite to be formed in such an acidic environment
(pH = 6)?
(though today, after being fed a normal food, the pH was 8.5!)

Whenever you find crystals in acid urine it means that either the urine is
not sufficiently acidified or insufficient time has elapsed for the crystals
to dissolve. If urine pH is high for any length of time crystals can form.

Also, a single determination of acidic urine does not mean the urine was
sufficiently acidic to be undersaturated with struvite before the
obstruction --- the fact that you found crystals proves it wasn't.

Another thing to remember is anorexia usually develops after cats devlop a
urethral obstruction - most cats aren't brought to vet for at least 24 hours
after their last meal -- this increases the probability that the urine pH
will be acidic when its tested.



2. how easy is it to determine wether it's struvite or calcium oxalate? in
the microscope there can be seen a variety of shapes and forms of crystals
(but not a great number of them). is there another more accurate method?


Optical crystallography, thermal analysis, infrared spectrophotometry,
electron microprobe analysis, x-ray diffraction, -- or a combination of
these methods. Microscopic examination only identifies the outside of a
urolith. Some uroliths have a mixed composition - IOW, they have a nucleus
composed of calcium oxalate and a shell composed of struvite. That's why
quantitative mineral analysis, rather than qualitive analysis is so
important.

Also, there's a big difference between struvite uroliths and struvite
urethral plugs. Uroliths are made up of mostly of magnesium ammonium
phosphate (MAP) and small amounts of matrix. Struvite plugs are usually
made up of large amounts of matrix mixed with small amounts of MAP.. Some
urethral plugs are made up of organic matrix, sloughed tissue, blood, and/or
debris, and others are form in association with an infection
(infection-induced struvite).

Plugs are more common in male cats than actual uroliths - which are more
common in females. If your cat has struvite plugs, the prescription diet
isn't going to help that much.

hth,

Phil